Generally, drawn arc fastener welding is performed using a constant current welding process with a fixed arc current and a fixed arc time as welding parameters that are maintained by a drawn arc stud welding power source. Other process variables include a lift height and plunge depth that are typically controlled by various mechanisms including mechanical mechanisms as well as electronically controlled devices. The lift height and weld puddle depression create an arc gap between the fastener and work piece, and the length of the arc gap and the ionization potential gradient of the arc plasma together with fixed anode and cathode drops establish an arc voltage. The product of the arc voltage and arc current is an arc power which may be multiplied by an arc time to compute an arc energy. The amount of arc energy serves as the heat source that melts both the fastener and the work piece. The resultant heat generated by the arc energy may have an effect on the process stability and weld quality performed in a welding operation.
As stated above, conventional drawn arc welding processes use a fixed arc current, arc time, lift height, and plunge depth in production regardless of various parameters associated with the work piece and process conditions. For example, the lift height may vary as a result of differences in the set-up of welding tools (for example hand guns) within a fabrication shop or manufacturing facility. Additionally, various work pieces may contain coatings such as zinc or other contamination such as a layer of oil or other material such as a rust or mill scale, or weldable primer paint. As a result, the heat input to both the fastener and work piece may vary and may result in inconsistency and lack of repeatability in weld quality, weld appearance or backside marking. There is therefore a need in the art for a drawn arc welding process that delivers a constant are energy for a particular welding application.